Polyurethane quasi prepolymer for proppant consolidation

Abstract

A method of preparing a consolidating agent in the form of a polyurethane prepolymer for consolidating a proppant in a subterranean formation about a well employing the improvement characterized by a quasi prepolymer formed by reacting a diol with a stoichiometric excess of isomeric methylene diphenylene diisocyanate and a diluent; and allowing the reactants to stand for a period in excess of two hours at 25 degrees C., whereby to form oligmers of polyurethane chains. The method enables consolidating a proppant in fractures by a slow polymerization process, whereby the curing agent can be added at the same time the proppant is placed. Also disclosed are specific examples of diluents and curing agents.

What is claimed is: 
     
       1. A method for forming a quasi prepolymer containing polyurethane linkages comprising: a. forming said quasi prepolymer by reacting in intimate admixture a diol and in stoichiometric excess methylene diphenylene diisocyanate, all in the presence of a diluent; and   b. allowing the reactants to stand in intimate admixture for a time sufficient to form oligmers containing polyurethane linkages.   
     
     
       2. The method of claim 1 wherein the weight ratio of the isomeric methylene diphenylene diisocyanate to the diol is within the range of 12:1 to 2:1. 
     
     
       3. The method of claim 1 wherein said diol is dipropylene glycol. 
     
     
       4. The method of claim 1 wherein said diluent is selected from the class consisting of dimethyl formamide, propylene carbonate, and dimethyl sulfoxide. 
     
     
       5. The method of claim 1 further comprising adding a catalyst to the quasi prepolymer resulting from step b. 
     
     
       6. The method of claim 5 wherein the catalyst added to the quasi prepolymer of step b. is selected from the group consisting of water and a strong base. 
     
     
       7. The method of claim 1 wherein a catalyst is employed and said catalyst is an organo metallic contained in a minor amount in a hydrocarbonaceous liquid. 
     
     
       8. The method of claim 1 wherein said catalyst is water in a proportion sufficient to effect a moisture cure after emplacement. 
     
     
       9. The method of claim 5 wherein a proppant is added as an inert filler to the quasi prepolymer and product admixture before injecting into a well. 
     
     
       10. The method of claim 9 wherein said proppant is sand and said sand is present in a proportion in the range of 95-98 percent by weight. 
     
     
       11. The method of claim 1 wherein said method is employed for consolidating a proppant injected in subterranean formations with a a curing agent, for production to the earth's surface via a well a desired hydrocarbonaceous fluid wherein said methylene diphenylene diisocyanate is an isomeric admixture of methylene diphenylene diisocyanate, and wherein said reactants are allowed to stand in intimate admixture for at least 2 hours at at least 25 degrees C.